This invention relates to ultrasound imaging systems, and in particular to a system and method for using multiline beams in an ultrasound imaging system to simultaneously obtain both flow and B-mode data, and/or Doppler data (flow, power, and/or tissue motion).
Ultrasound scanning systems operate in various imaging modes, depending on the type of image that is desired, the subject being imaged, the constraints of the system itself, etc. The formation of three-dimensional (3D) volumes of ultrasound data in real time strictly limits the number of transmit/receive cycles available for sampling the region to be imaged. The same is true for high frame rate, large field-of-view two-dimensional (2D) applications.
Multiline (or parallel) imaging is a relatively efficient use of transmit cycles because it allows one to obtain multiple receive lines for each transmit event. The basic premise of multiline imaging is to use parallel processing paths to receive multiple beams along adjacent, but spatially distinct, paths from a single transmit event. A single transmit beam is emitted, and parallel beamforming simultaneously receives echo beams along either side (and/or top and bottom for 3D data) of the transmit beam. B-Mode data, which is indicative of the amplitude of the received echoes, may be obtained and displayed (and/or stored) from the received multiline echoes as known in the art. 2xc3x97multiline receives one beam on either side of the transmit beam, 4xc3x97multiline receives 2 beams on either side, etc. With a 2D array, one can extend the multiline concept into the elevation direction by receiving beam on both sides, top, bottom and diagonally from the transmit beam.
Obtaining flow or motion information requires multiple transmit-receive cycles from the same anatomic region. B-flow imaging is an example of using a minimum number of transmit events (typically two) to obtain flow information. The most straightforward option for producing B-flow images using 2xc3x97multiline is to transmit two sequential beams along the same line and then subtract the second pair of received echoes from the first pair of received echoes. This provides the same number of received flow lines as transmit lines and a flow line density that is twice the transmit line density, so it is possible to reduce the transmit line density to compensate for the need to transmit twice down each line. By combining received echoes from addition transmit lines down the same path, this concept can easily be extended to more complex forms of Doppler flow signal processing, such as tissue and blood velocity and power Doppler.
It is desired to be able to optimize ultrasound imaging techniques in order to obtain as much data as possible and provide as much insight as possible regarding a subject being imaged. The present invention addresses this need by providing flow or motion data and B-mode data from the same set of received echoes as explained herein.
The present invention is directed to an ultrasound imaging system and method that simultaneously forms a B-mode volume and B-flow volume from the same set of transmit beams. When forming 3D volumes, the image data is usually reduced to a lower sampling density than the original image data (typically a maximum of 256 samples in any dimension, given current processing capabilities). Thus, limitations in image quality or flow quality due to tradeoffs for efficiency can be tolerated to some degree.
This invention is possible if the receive lines between two adjacent transmit lines are steered to overlap to a large degree and the transmit beams are broad enough to overlap to some degree, so that there is some degree of spatial coherence. Processing them would then form a B-flow line, with the quality of the flow signal being dependent on the degree of spatial coherence between the two receive lines and the velocity range being dependent on the amount of time between the adjacent transmit cycles, both of which can be controlled by the system design. If more overlapping transmit beams are fired, more complex Doppler processing is possible.
Thus, in a first major aspect of the invention, the present invention is a method of and system for imaging an object with an ultrasound transducer array that transmits ultrasound beams and detects echoes reflected from the object. A plurality of adjacent ultrasound beams are transmitted at the object, each of the beams being separated from an adjacent beam by a first predetermined distance. A plurality of groups of echoes are received from the object, with each of the groups of echoes corresponding to one of the plurality of the transmitted ultrasound beams. Each of these echoes is spaced from the corresponding transmitted ultrasound beam by a second predetermined distance which is less than the first predetermined distance. The transmitted ultrasound beams are arranged such that one of the received echoes corresponding to one transmitted ultrasound beam substantially overlaps with one of the received echoes corresponding to an adjacent transmitted ultrasound beam. At least a subset of the received echoes are then processed to obtain B-mode data from each of the processed echoes. In addition, the overlapping pairs of received echoes are processed to obtain B-flow data, typically by determining the difference between the overlapping received echoes. In a preferred embodiment, each group of echoes comprises a pair of echoes.
In a second major aspect of the invention, the present invention is a method of and system for imaging an object with an ultrasound transducer array that transmits ultrasound beams and detects echoes reflected from the object. A plurality of pairs of adjacent ultrasound beams are transmitted at the object, each of the pairs of beams separated from an adjacent pair of beams by a first predetermined distance. Each pair of beams includes a positive polarity pulse beam and a negative polarity pulse beam, with the positive polarity pulse beam being transmitted in the same space as the negative polarity pulse beam. A plurality of pairs of echoes are received from the object, with each of the pairs of echoes corresponding to one of the plurality of transmitted ultrasound beams. Each pair of echoes includes a first received echo and a second received echo, with each of these echoes spaced from the corresponding transmitted ultrasound beam by a second predetermined distance which is less than the first predetermined distance. The transmitted ultrasound beams are arranged such that one of the received echoes corresponding to one transmitted ultrasound beam substantially overlaps with one of the received echoes corresponding to an adjacent ultrasound beam. At least a subset of the received echoes are then processed to obtain B-mode data from each of the processed echoes. In addition, the overlapping pairs of received echoes are processed to obtain B-flow data. The B-Mode processing utilizes harmonic filtering techniques on the opposite polarity echoes.
Doppler flow data, power data, and/or tissue motion data may also be processed, displayed and/or stored via the data acquisition techniques of this invention.